Approach to measure thin film layers, nanometer scale, on surfaces through non-contact capacitive proximity sensor

ABSTRACT

An ultra-high resolution capacitive sensor affixed above an imaging member surface measures the thickness of fountain solution on the imaging member surface in real-time during a printing operation. The sensor is considered ultra-high resolution with a resolution high enough to detect nanometer scale thicknesses. The capacitive sensor would initially be zeroed to the imaging member surface. As fluid is added, the capacitive sensor detects the increase and can measure and communicate with the image forming device to adjust fountain solution flow rate to the imaging member surface and correct for any anomalies in thickness. This fountain solution monitoring system may be fully automated. The capacitive sensor may have a resolution (e.g., as low as about 1 nm resolution) of about 0.001% of the distance/gap that the capacitive sensor is mounted away from the imaging member surface.

FIELD OF DISCLOSURE

This invention relates generally to digital printing systems, and moreparticularly, to fountain solution deposition systems and methods foruse in lithographic offset printing systems.

BACKGROUND

Conventional lithographic printing techniques cannot accommodate truehigh speed variable data printing processes in which images to beprinted change from impression to impression, for example, as enabled bydigital printing systems. The lithography process is often relied upon,however, because it provides very high quality printing due to thequality and color gamut of the inks used. Lithographic inks are alsoless expensive than other inks, toners, and many other types of printingor marking materials.

Ink-based digital printing uses a variable data lithography printingsystem, or digital offset printing system, or a digital advancedlithography imaging system. A “variable data lithography system” is asystem that is configured for lithographic printing using lithographicinks and based on digital image data, which may be variable from oneimage to the next. “Variable data lithography printing,” or “digitalink-based printing,” or “digital offset printing,” or digital advancedlithography imaging is lithographic printing of variable image data forproducing images on a substrate that are changeable with each subsequentrendering of an image on the substrate in an image forming process.

For example, a digital offset printing process may include transferringink onto a portion of an imaging member (e.g., fluorosilicone-containingimaging member, printing plate) having a surface or imaging blanket thathas been selectively coated with a fountain solution (e.g., dampeningfluid) layer according to variable image data. According to alithographic technique, referred to as variable data lithography, anon-patterned reimageable surface of the imaging member is initiallyuniformly coated with the fountain solution layer. An imaging systemthen evaporates regions of the fountain solution layer in an image areaby exposure to a focused radiation source (e.g., a laser light source,high power laser) to form pockets. A temporary pattern latent image inthe fountain solution is thereby formed on the surface of the digitaloffset imaging member. The latent image corresponds to a pattern of theapplied fountain solution that is left over after evaporation. Inkapplied thereover is retained in the pockets where the laser hasvaporized the fountain solution. Conversely, ink is rejected by theplate regions where fountain solution remains. The inked surface is thenbrought into contact with a substrate at a transfer nip and the inktransfers from the pockets in the fountain solution layer to thesubstrate. The fountain solution may then be removed, a new uniformlayer of fountain solution applied to the printing plate, and theprocess repeated.

Digital printing is generally understood to refer to systems and methodsof variable data lithography, in which images may be varied amongconsecutively printed images or pages. “Variable data lithographyprinting,” or “ink-based digital printing,” or “digital offset printing”are terms generally referring to printing of variable image data forproducing images on a plurality of image receiving media substrates, theimages being changeable with each subsequent rendering of an image on animage receiving media substrate in an image forming process. “Variabledata lithographic printing” includes offset printing of ink imagesgenerally using specially-formulated lithographic inks, the images beingbased on digital image data that may vary from image to image, such as,for example, between cycles of an imaging member having a reimageablesurface. Examples are disclosed in U.S. Patent Application PublicationNo. 2012/0103212 A1 (the '212 Publication) published May 3, 2012 basedon U.S. patent application Ser. No. 13/095,714, and U.S. PatentApplication Publication No. 2012/0103221 A1 (the '221 Publication) alsopublished May 3, 2012 based on U.S. patent application Ser. No.13/095,778.

The inventors have found that digital printing processes are sensitiveto the amount of fountain solution applied to the imaging memberblanket. If too much fountain solution is applied to the imaging membersurface, then the laser may not be able to boil/evaporate the fountainsolution and no image will be created on the blanket. If too littlefountain solution is applied to the imaging member surface, then the inkwill not be rejected in the non-imaged regions leading to highbackground. Currently, there is no way to measure how much fountainsolution is deposited on the imaging member blanket in real-time duringa printing operation. Further, current fountain solution systems operateopen loop, where the amount of fountain solution is manually adjustablebased on image quality of previous print jobs. In this state, fountainsolution systems are at the mercy of printing device noises and mayrequire constant manual adjustments.

SUMMARY

The following presents a simplified summary in order to provide a basicunderstanding of some aspects of one or more embodiments or examples ofthe present teachings. This summary is not an extensive overview, nor isit intended to identify key or critical elements of the presentteachings, nor to delineate the scope of the disclosure. Rather, itsprimary purpose is merely to present one or more concepts in simplifiedform as a prelude to the detailed description presented later.Additional goals and advantages will become more evident in thedescription of the figures, the detailed description of the disclosure,and the claims.

The foregoing and/or other aspects and utilities embodied in the presentdisclosure may be achieved by providing a method of controlling fountainsolution thickness on an imaging member surface of a rotating imagingmember in a digital image forming device. The method includes measuringa first capacitance between a capacitive proximity sensor spatiallyoffset a fixed distance from the imaging member surface and the imagingmember surface having no fluid therebetween, applying a fountainsolution fluid layer at a dispense rate onto the imaging member surfaceupstream the capacitive proximity sensor in an image making directionfor rendering a printing, measuring a second capacitance between thecapacitive proximity sensor and the imaging member surface with thefountain solution layer therebetween and spatially distanced from thecapacitive proximity sensor, comparing a difference between the firstcapacitance and the second capacitance to a predefined targetcapacitance, modifying the fountain solution dispense rate based on thecomparison, and applying a subsequent fountain solution layer at themodified fountain solution dispense rate onto the imaging member surfaceupstream the capacitive proximity sensor for rendering a subsequentprinting.

According to aspects illustrated herein, an exemplary method ofcontrolling fountain solution thickness on an imaging member surface ofa rotating imaging member in a digital image forming device isdescribed, with the digital image forming device configured to print acurrent image onto a print substrate. The printing operation includesapplying a fountain solution layer at a dispense rate onto the imagingmember surface, vaporizing in an image wise fashion a portion of thefountain solution layer to form a latent image, applying ink onto thelatent image over the imaging member surface, and transferring theapplied ink from the imaging member surface to the print substrate. Themethod includes measuring a capacitance between a capacitive proximitysensor and the imaging member surface with the fountain solution layertherebetween and spatially distanced from the capacitive proximitysensor, comparing a difference between the measured capacitance and areference capacitance between the imaging member surface and thecapacitive proximity sensor, to a target capacitance, and modifying thefountain solution dispense rate based on the comparison for a subsequentprinting of a subsequent image by the digital image forming device usingthe modified fountain solution dispense rate.

According to aspects described herein, an exemplary digital imageforming device controls fountain solution thickness on an imaging membersurface of a rotating imaging member. The digital image forming deviceincludes a capacitive sensor, a fountain solution applicator, and acontroller. The capacitance sensor is distanced from the imaging membersurface forming a gap therebetween, with the capacitance sensorconfigured to measure a first capacitance between the capacitiveproximity sensor and the imaging member surface with the imaging membersurface having no fluid therebetween. The fountain solution applicatoris configured to apply a fountain solution fluid layer at a dispenserate onto the imaging member surface upstream the capacitive proximitysensor in an image making direction for rendering a printing. Thecapacitance sensor is configured to measure a second capacitance betweenthe capacitive proximity sensor and the imaging member surface with thefountain solution layer therebetween and spatially distanced from thecapacitive proximity sensor. The controller is in communication with thecapacitance sensor to compare a difference between the first capacitanceand the second capacitance to a predefined target capacitance, and tomodify the fountain solution dispense rate based on the comparison. Thefountain solution applicator is configured to apply a subsequentfountain solution layer at the modified fountain solution dispense rateonto the imaging member surface upstream the capacitive proximity sensorfor rendering a subsequent printing.

Exemplary embodiments are described herein. It is envisioned, however,that any system that incorporates features of apparatus and systemsdescribed herein are encompassed by the scope and spirit of theexemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of the disclosed apparatuses, mechanismsand methods will be described, in detail, with reference to thefollowing drawings, in which like referenced numerals designate similaror identical elements, and:

FIG. 1 is block diagram of a digital image forming device in accordancewith examples of the embodiments;

FIG. 2 is a perspective view of an exemplary fountain solutionapplicator;

FIG. 3 is a block diagram of a capacitive sensor spatially distancedfrom a fountain solution layer on an imaging member surface;

FIG. 4 is a block diagram of a controller for executing instructions tocontrol the digital image forming device; and

FIG. 5 is a flowchart depicting the operation of an exemplary imageforming device.

DETAILED DESCRIPTION

Illustrative examples of the devices, systems, and methods disclosedherein are provided below. An embodiment of the devices, systems, andmethods may include any one or more, and any combination of, theexamples described below. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth below. Rather, these exemplary embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Accordingly, the exemplary embodiments are intended to cover allalternatives, modifications, and equivalents as may be included withinthe spirit and scope of the apparatuses, mechanisms and methods asdescribed herein.

We initially point out that description of well-known startingmaterials, processing techniques, components, equipment and otherwell-known details may merely be summarized or are omitted so as not tounnecessarily obscure the details of the present disclosure. Thus, wheredetails are otherwise well known, we leave it to the application of thepresent disclosure to suggest or dictate choices relating to thosedetails. The drawings depict various examples related to embodiments ofillustrative methods, apparatus, and systems for inking from an inkingmember to the reimageable surface of a digital imaging member.

When referring to any numerical range of values herein, such ranges areunderstood to include each and every number and/or fraction between thestated range minimum and maximum. For example, a range of 0.5-6% wouldexpressly include the endpoints 0.5% and 6%, plus all intermediatevalues of 0.6%, 0.7%, and 0.9%, all the way up to and including 5.95%,5.97%, and 5.99%. The same applies to each other numerical propertyand/or elemental range set forth herein, unless the context clearlydictates otherwise.

The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (forexample, it includes at least the degree of error associated with themeasurement of the particular quantity). When used with a specificvalue, it should also be considered as disclosing that value. Forexample, the term “about 2” also discloses the value “2” and the range“from about 2 to about 4” also discloses the range “from 2 to 4.”

The term “controller” or “control system” is used herein generally todescribe various apparatus such as a computing device relating to theoperation of one or more device that directs or regulates a process ormachine. A controller can be implemented in numerous ways (e.g., such aswith dedicated hardware) to perform various functions discussed herein.A “processor” is one example of a controller which employs one or moremicroprocessors that may be programmed using software (e.g., microcode)to perform various functions discussed herein. A controller may beimplemented with or without employing a processor, and also may beimplemented as a combination of dedicated hardware to perform somefunctions and a processor (e.g., one or more programmed microprocessorsand associated circuitry) to perform other functions. Examples ofcontroller components that may be employed in various embodiments of thepresent disclosure include, but are not limited to, conventionalmicroprocessors, application specific integrated circuits (ASICs), andfield-programmable gate arrays (FPGAs).

Embodiments as disclosed herein may also include computer-readable mediafor carrying or having computer-executable instructions or datastructures stored thereon. Such computer-readable media can be anyavailable media that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium which can be used to carry or store desiredprogram code means in the form of computer-executable instructions ordata structures. When information is transferred or provided over anetwork or another communications connection (either hardwired,wireless, or combination thereof) to a computer, the computer properlyviews the connection as a computer-readable medium. Thus, any suchconnection is properly termed a computer-readable medium. Combinationsof the above should also be included within the scope of thecomputer-readable media.

Computer-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Computer-executable instructions also includeprogram modules that are executed by computers in stand-alone or networkenvironments. Generally, program modules include routines, programs,objects, components, and data structures, and the like that performparticular tasks or implement particular abstract data types.Computer-executable instructions, associated data structures, andprogram modules represent examples of the program code means forexecuting steps of the methods disclosed herein. The particular sequenceof such executable instructions or associated data structures representsexamples of corresponding acts for implementing the functions describedtherein.

Although embodiments of the invention are not limited in this regard,discussions utilizing terms such as, for example, “processing,”“computing,” “calculating,” “determining,” “using,” “establishing”,“analyzing”, “checking”, or the like, may refer to operation(s) and/orprocess(es) of a controller, computer, computing platform, computingsystem, or other electronic computing device, that manipulate and/ortransform data represented as physical (e.g., electronic) quantitieswithin the computer's registers and/or memories into other datasimilarly represented as physical quantities within the computer'sregisters and/or memories or other information storage medium that maystore instructions to perform operations and/or processes.

The terms “media”, “print media”, “print substrate” and “print sheet”generally refers to a usually flexible physical sheet of paper, polymer,Mylar material, plastic, or other suitable physical print mediasubstrate, sheets, webs, etc., for images, whether precut or web fed.The listed terms “media”, “print media”, “print substrate” and “printsheet” may also include woven fabrics, non-woven fabrics, metal films,and foils, as readily understood by a skilled artisan.

The term “image forming device”, “printing device” or “printing system”as used herein may refer to a digital copier or printer, scanner, imageprinting machine, xerographic device, electrostatographic device,digital production press, document processing system, image reproductionmachine, bookmaking machine, facsimile machine, multi-function machine,or generally an apparatus useful in performing a print process or thelike and can include several marking engines, feed mechanism, scanningassembly as well as other print media processing units, such as paperfeeders, finishers, and the like. A “printing system” may handle sheets,webs, substrates, and the like. A printing system can place marks on anysurface, and the like, and is any machine that reads marks on inputsheets; or any combination of such machines.

The term “fountain solution” or “dampening fluid” refers to dampeningfluid that may coat or cover a surface of a structure (e.g., imagingmember, transfer roll) of an image forming device to affect connectionof a marking material (e.g., ink, toner, pigmented or dyed particles orfluid) to the surface. The fountain solution may include wateroptionally with small amounts of additives (e.g., isopropyl alcohol,ethanol) added to reduce surface tension as well as to lower evaporationenergy necessary to support subsequent laser patterning. Low surfaceenergy solvents, for example volatile silicone oils, can also serve asfountain solutions. Fountain solutions may also include wettingsurfactants, such as silicone glycol copolymers. The fountain solutionmay include D4 or D5 dampening fluid alone, mixed, and/or with wettingagents. The fountain solution may also include Isopar G, Isopar H,Dowsil OS20, Dowsil OS30, and mixtures thereof.

Inking systems or devices may be incorporated into a digital offsetimage forming device architecture so that the inking system is arrangedabout a central imaging plate, also referred to as an imaging member. Insuch a system, the imaging member is a rotatable imaging member,including a conformable blanket around a central drum with theconformable blanket including the reimageable surface. This blanketlayer has specific properties such as composition, surface profile, andso on so as to be well suited for receipt and carrying a layer of afountain solution. A surface of the imaging member is reimageable makingthe imaging member a digital imaging member. The surface is constructedof elastomeric materials and conformable. A paper path architecture maybe situated adjacent the imaging member to form a media transfer nip.

A layer of fountain solution may be applied to the surface of theimaging member by a dampening system. In a digital evaporation step,particular portions of the fountain solution layer deposited onto thesurface of the imaging member may be evaporated by a digital evaporationsystem. For example, portions of the fountain solution layer may bevaporized by an optical patterning subsystem such as a scanned,modulated laser that patterns the fluid solution layer to form a latentimage. In a vapor removal step, the vaporized fountain solution may becollected by a vapor removal device or vacuum to prevent condensation ofthe vaporized fountain solution back onto the imaging plate.

In an inking step, ink may be transferred from an inking system to thesurface of the imaging member such that the ink selectively resides inevaporated voids formed by the patterning subsystem in the fountainsolution layer to form an inked image. In an image transfer step, theinked image is then transferred to a print substrate such as paper viapressure at the media transfer nip.

In a digital variable printing process, previously imaged ink must beremoved from the imaging member surface to prevent ghosting. After animage transfer step, the surface of the imaging member may be cleaned bya cleaning system so that the printing process may be repeated. Forexample, tacky cleaning rollers may be used to remove residual ink andfountain solution from the surface of the imaging member.

A drawback of digital print processes is print quality sensitivity tothe amount of fountain solution deposited onto the imaging blanket. Itis estimated that a very thin layer of fountain solution (e.g., 30-100nm thickness range) is required on the blanket for optimal print processsetup. This makes measuring the fountain solution thickness on theimaging blanket most difficult.

FIG. 1 depicts an exemplary ink-based digital image forming device 10.The image forming device 10 may include dampening station 12 havingfountain solution applicator 14, optical patterning subsystem 16, inkingapparatus 18, and a cleaning device 20. The image forming device 10 mayalso include one or more rheological conditioning subsystems 22 asdiscussed, for example, in greater detail below. FIG. 1 shows thefountain solution applicator 14 arranged with a digital imaging member24 having a reimageable surface 26. While FIG. 1 shows components thatare formed as rollers, other suitable forms and shapes may beimplemented.

The imaging member surface 26 may be wear resistant and flexible. Thesurface 26 may be reimageable and conformable, having an elasticity anddurometer, and sufficient flexibility for coating ink over a variety ofdifferent media types having different levels of roughness. A thicknessof the reimageable surface layer may be, for example, about 0.5millimeters to about 4 millimeters. The surface 26 should have a weakadhesion force to ink, yet good oleophilic wetting properties with theink for promoting uniform inking of the reimageable surface andsubsequent transfer lift of the ink onto a print substrate.

The soft, conformable surface 26 of the imaging member 24 may include,for example, hydrophobic polymers such as silicones, partially or fullyfluorinated fluorosilicones and FKM fluoroelastomers. Other materialsmay be employed, including blends of polyurethanes, fluorocarbons,polymer catalysts, platinum catalyst, hydrosilyation catalyst, etc. Thesurface may be configured to conform to a print substrate on which anink image is printed. To provide effective wetting of fountain solutionssuch as water-based dampening fluid, the silicone surface need not behydrophilic, but may be hydrophobic. Wetting surfactants, such assilicone glycol copolymers, may be added to the fountain solution toallow the fountain solution to wet the reimageable surface 26. Theimaging member 24 may include conformable reimageable surface 26 of ablanket or belt wrapped around a roll or drum. The imaging membersurface 26 may be temperature controlled to aid in a printing operation.For example, the imaging member 24 may be cooled internally (e.g., withchilled fluid) or externally (e.g., via a blanket chiller roll 28 to atemperature (e.g., about 10° C.-60° C.) that may aid in the imageforming, transfer and cleaning operations of image forming device 10.

The reimageable surface 26 or any of the underlying layers of thereimageable belt/blanket may incorporate a radiation sensitive fillermaterial that can absorb laser energy or other highly directed energy inan efficient manner. Examples of suitable radiation sensitive materialsare, for example, microscopic (e.g., average particle size less than 10micrometers) to nanometer sized (e.g., average particle size less than1000 nanometers) carbon black particles, carbon black in the form ofnano particles of, single or multi-wall nanotubes, graphene, iron oxidenano particles, nickel plated nano particles, etc., added to the polymerin at least the near-surface region. It is also possible that no fillermaterial is needed if the wavelength of a laser is chosen so to match anabsorption peak of the molecules contained within the fountain solutionor the molecular chemistry of the outer surface layer. As an example, a2.94 μm wavelength laser would be readily absorbed due to the intrinsicabsorption peak of water molecules at this wavelength.

The fountain solution applicator 14 may be configured to deposit a layerof fountain solution onto the imaging member surface 26 directly or viaan intermediate member (e.g., roller 30) of the dampening station 12.While not being limited to particular configuration, the fountainsolution applicator 14 may include a series of rollers, sprays or avaporizer (not shown) for uniformly wetting the reimageable surface 26with a uniform layer of fountain solution with the thickness of thelayer being controlled. The series of rollers may be considered asdampening rollers or a dampening unit, for uniformly wetting thereimageable surface 26 with a layer of fountain solution. The fountainsolution may be applied by fluid or vapor deposition to create a thinfluid layer 32 (e.g., between about 0.01 μm and about 1.0 μm inthickness, less than 5 μm, about 50 nm to 100 nm) of the fountainsolution for uniform wetting and pinning. The vaporizer may include aslot at its output across the imaging member 26 or intermediate roller30 to output vapor fountain solution to the imaging member surface 26.

FIG. 2 depicts another exemplary fountain solution applicator 14 thatmay apply a fountain solution layer directly onto the imaging membersurface 26. The fountain solution applicator 14 includes a supplychamber 62 that may be generally cylindrical defining an interior forcontaining fountain solution vapor therein. The supply chamber 62includes an inlet tube 64 in fluid communication with a fountainsolution supply (not shown), and a tube portion 66 extending to a closeddistal end 68 thereof. A supply channel 70 extends from the supplychamber 62 to adjacent the imaging member surface 26, with the supplychannel defining an interior in communication with the interior of thesupply chamber to enable flow of fountain solution vapor from the supplychamber through the supply channel and out a supply channel outlet slot72 for deposition over the imaging member surface, where the fountainsolution vapor condenses to a fluid on the imaging member surface.

A vapor flow restriction boarder 74 extends from the supply channel 70adjacent the reimageable surface 26 to confine fountain solution vaporprovided from the supply channel outlet slot 72 to a condensation regiondefined by the restriction boarder and the adjacent reimageable surfaceto support forming a layer of fountain solution on the reimageablesurface via condensation of the fountain solution vapor onto thereimageable surface. The restriction boarder 74 defines the condensationregion over the surface 26 of the imaging member 24. The restrictionboarder includes arc walls 76 that face the imaging member surface 26,and boarder wall 78 that extends from the arc walls towards the imagingmember surface. The reimageable surface 26 of the imaging member 24 mayhave a width W parallel to the supply channel 70 and supply channeloutlet slot 72, with the outlet slot having a width across the imagingmember configured to enable fountain solution vapor in the supplychamber interior to communicate with the imaging member surface acrossits width.

As noted above, currently there is no way to measure how much fountainsolution is deposited on the imaging member blanket surface 26 inreal-time during a printing operation. One drawback in trying to measurethe thickness of fountain solution directly on the imaging blanket isthat the top surface of the blanket is coated with afluorosilicone/carbon black solution. The carbon black is added toabsorb the laser light during the imaging process. The carbon black alsomakes it very difficult to measure the fountain solution on the blanketduring image forming operations using a non-contact specular sensorbecause light is absorbed by the blanket. Such specular sensorsresearched as potential solutions have been very expensive. Anadditional drawback of the fluorosilicone/carbon black imaging membersurface is that any contact sensors scuff/abrade the surface causingdefects objectionable in the print. As a solution to the drawback, theinventors found that instead of measuring the thickness of fountainsolution directly on the imaging blanket, results of a current printingon a print substrate may be used to determine the fountain solutionthickness applied during the rendering of the current printing, and todetermine corrective action to modify fountain solution applicationduring subsequent printings to reach a desired thickness.

Referring back to FIG. 1, the inventors found that an ultra-highresolution capacitive sensor 58 (e.g., capacitive proximity sensor,non-contact high resolution capacitive displacement sensor) affixedabove an imaging member surface (e.g., less than a few microns, lessthan 20 μm, less than 50 μm, less than 100 μm, less than 750 microns)can measure the thickness of fountain solution on the imaging membersurface in real-time during a printing operation. The capacitive sensor58 may be single electrode and considered ultra-high resolution with aresolution high enough to detect nanometer scale thicknesses. Thecapacitive sensor may have more than one electrode. The capacitivesensor 58 would initially be zeroed to the imaging member surface. Asfountain solution layer 32 is added, the capacitive sensor detects theincrease and can measure and communicate with the image forming deviceto adjust fountain solution flow rate to the imaging member surface andcorrect for any anomalies in thickness. This fountain solutionmonitoring system may be fully automated. The capacitive sensor 58 mayhave a resolution (e.g., as low as about 1 nm resolution) of about0.001% of the distance/gap that the capacitive sensor is mounted awayfrom the imaging member surface. The capacitive sensor 58 is also shownin FIG. 3, which depicts the capacitive sensor spatially distanced fromfountain solution layer 32 on the imaging member surface 26 of imagingmember 24.

Fountain solution layer 32 thickness quality control monitoring may beapplied on line during the printing process instead of periodic samplingafter the printing has been manufactured. This way fountain solutionflow rate adjustment can be made “on the fly”, reducing or eliminatingthe production of printings having undesired lessened quality. Thecapacitive sensor 58 operates by measuring changes in position. Whenmaking these types of measurements a fixed gap is established betweenthe capacitive sensor 58 and a grounded plate, here the imaging membersurface 26. Fountain solution placed between the capacitive sensor andthe imaging member surface 26 displaces air which a dielectric constantdifferent than the fountain solution. Thus when fountain solution isinserted in this gap the capacitance will change even if the distancebetween the capacitive sensor 58 and the imaging member surface 26remain constant. This change will create a change in the voltage outputof the amplifier proportional to the fountain solution layer 32thickness. The capacitance changes can then be measured with thecapacitive sensor 58 and correlated with the fountain solution layer 32thickness.

Still referring to FIG. 1 the optical patterning subsystem 16 is locateddownstream the fountain solution applicator 14 in the printingprocessing direction to selectively pattern a latent image in the layerof fountain solution by image-wise patterning using, for example, laserenergy. For example, the fountain solution layer is exposed to an energysource (e.g. a laser) that selectively applies energy to portions of thelayer to image-wise evaporate the fountain solution and create a latent“negative” of the ink image that is desired to be printed on a receivingsubstrate 34. Image areas are created where ink is desired, andnon-image areas are created where the fountain solution remains. Whilethe optical patterning subsystem 16 is shown as including laser emitter36, it should be understood that a variety of different systems may beused to deliver the optical energy to pattern the fountain solutionlayer.

A vapor vacuum 38 or air knife may be positioned downstream the opticalpatterning subsystem to collect vaporized fountain solution and thusavoid leakage of excess fountain solution into the environment.Reclaiming excess vapor prevents fountain solution from depositinguncontrollably prior to the inking apparatus 18 and imaging member 24interface. The vapor vacuum 38 may also prevent fountain solution vaporfrom entering the environment. Reclaimed fountain solution vapor can becondensed, filtered and reused as understood by a skilled artisan tohelp minimize the overall use of fountain solution by the image formingdevice 10.

Following patterning of the fountain solution layer by the opticalpatterning subsystem 16, the patterned layer over the reimageablesurface 26 is presented to the inking apparatus 18. The inker apparatus18 is positioned downstream the optical patterning subsystem 16 to applya uniform layer of ink over the layer of fountain solution and thereimageable surface layer 26 of the imaging member 24. The inkingapparatus 18 may deposit the ink to the evaporated pattern representingthe imaged portions of the reimageable surface 26, while ink depositedon the unformatted portions of the fountain solution will not adherebased on a hydrophobic and/or oleophobic nature of those portions. Theinking apparatus may heat the ink before it is applied to the surface 26to lower the viscosity of the ink for better spreading into imagedportion pockets of the reimageable surface. For example, one or morerollers 40 of the inking apparatus 18 may be heated, as well understoodby a skilled artisan. Inking roller 40 is understood to have a structurefor depositing marking material onto the reimageable surface layer 26,and may include an anilox roller or an ink nozzle. Excess ink may bemetered from the inking roller 40 back to an ink container 42 of theinker apparatus 18 via a metering member 44 (e.g., doctor blade, airknife).

Although the marking material may be an ink, such as a UV-curable ink,the disclosed embodiments are not intended to be limited to such aconstruct. The ink may be a UV-curable ink or another ink that hardenswhen exposed to UV radiation. The ink may be another ink having acohesive bond that increases, for example, by increasing its viscosity.For example, the ink may be a solvent ink or aqueous ink that thickenswhen cooled and thins when heated.

Downstream the inking apparatus 18 in the printing process directionresides ink image transfer station 46 that transfers the ink image fromthe imaging member surface 26 to a print substrate 34. The transferoccurs as the substrate 34 is passed through a transfer nip 48 betweenthe imaging member 24 and an impression roller 50 such that the inkwithin the imaged portion pockets of the reimageable surface 26 isbrought into physical contact with the substrate 34 and transfers viapressure at the transfer nip from the imaging member surface to thesubstrate as a print of the image.

Rheological conditioning subsystems 22 may be used to increase theviscosity of the ink at specific locations of the digital offset imageforming device 10 as desired. While not being limited to a particulartheory, rheological conditioning subsystem 22 may include a curingmechanism 52, such as a UV curing lamp (e.g., standard laser, UV laser,high powered UV LED light source), wavelength tunable photoinitiator, orother UV source, that exposes the ink to an amount of UV light (e.g., #of photons radiation) to at least partially cure the ink/coating to atacky or solid state. The curing mechanism may include various forms ofoptical or photo curing, thermal curing, electron beam curing, drying,or chemical curing. In the exemplary image forming device 10 depicted inFIG. 1, rheological conditioning subsystem 22 may be positioned adjacentthe substrate 34 downstream the ink image transfer station 46 to curethe ink image transferred to the substrate. Rheological conditioningsubsystems 22 may also be positioned adjacent the imaging member surface26 between the ink image transfer station 46 and cleaning device 20 as apreconditioner to harden any residual ink 54 for easier removal from theimaging member surface 26 that prepares the surface to repeat thedigital image forming operation.

This residual ink removal is most preferably undertaken without scrapingor wearing the imageable surface of the imaging member. Removal of suchremaining fluid residue may be accomplished through use of some form ofcleaning device 20 adjacent the surface 26 between the ink imagetransfer station 46 and the fountain solution applicator 14. Such acleaning device 20 may include at least a first cleaning member 56 suchas a sticky or tacky roller in physical contact with the imaging membersurface 26, with the sticky or tacky roller removing residual fluidmaterials (e.g., ink, fountain solution) from the surface. The sticky ortacky roller may then be brought into contact with a smooth roller (notshown) to which the residual fluids may be transferred from the stickyor tacky member, the fluids being subsequently stripped from the smoothroller by, for example, a doctor blade or other like device andcollected as waste. It is understood that the cleaning device 20 is oneof numerous types of cleaning devices and that other cleaning devicesdesigned to remove residual ink/fountain solution from the surface ofimaging member 24 are considered within the scope of the embodiments.For example, the cleaning device could include at least one roller,brush, web, belt, tacky roller, buffing wheel, etc., as well understoodby a skilled artisan.

In the image forming device 10, functions and utility provided by thedampening station 12, optical patterning subsystem 16, inking apparatus18, cleaning device 20, rheological conditioning subsystems 22, imagingmember 24 and capacitance sensor 58 may be controlled, at least in partby controller 60. Such a controller 60 is shown in FIGS. 1 and 4, andmay be further designed to receive information and instructions from aworkstation or other image input devices (e.g., computers, smart phones,laptops, tablets, kiosk) to coordinate the image formation on the printsubstrate through the various subsystems such as the dampening station12, patterning subsystem 16, inking apparatus 18, imaging member 24 andcapacitance sensor 58 as discussed in greater detail below andunderstood by a skilled artisan.

Based on the response data shown, by example, in FIG. 3 and/or stored asa lookup table, the controller can determine the fountain solutionthickness resulting on the imaging member surface 26. The controller 60may calculate the fountain solution thickness and adjust the fountainsolution flow rate accordingly. The controller 60 may also access alookup table (LUT) in data storage device 84 (FIG. 4) based on measuredcapacitances and initial measured capacitances and target capacitancesstored in the LUT. Further, the controller 60 may access the LUT todetermine an amount of modification of the fountain solution flow rateis needed to reach or maintain the desired fountain solution layerthickness.

While measurement of the fountain solution thickness is not required forthe print process discussed herein including modifying fountain solutiondeposition in real time based on measured capacitance and differences incapacitance, the inventors found it is highly desirable to measuresignals that directly correlate to the fountain solution thickness. Tothis end, the digital image forming device 10 can control fountainsolution thickness on the imaging member surface 26 regardless ofknowing the actual thickness. For example, upon knowing the initialcapacitance between the capacitive sensor 58 and the imaging membersurface 26, the capacitive sensor may measure the difference incapacitance from the initial capacitance and a capacitive measurement ofthe fountain solution layer. The controller 60 may then compare thedifference with a reference capacitance corresponding to the desiredfountain solution layer thickness and modify the fountain solutiondispense or flow rate accordingly.

FIG. 4 illustrates a block diagram of the controller 60 for executinginstructions to automatically control the digital image forming device10 and components thereof. The exemplary controller 60 may provide inputto or be a component of a controller for executing the image formationmethod including controlling fountain solution thickness in a systemsuch as that depicted in FIGS. 1-3 and 5, and described in greaterdetail below.

The exemplary controller 60 may include an operating interface 80 bywhich a user may communicate with the exemplary control system. Theoperating interface 80 may be a locally-accessible user interfaceassociated with the digital image forming device 10. The operatinginterface 80 may be configured as one or more conventional mechanismcommon to controllers and/or computing devices that may permit a user toinput information to the exemplary controller 60. The operatinginterface 80 may include, for example, a conventional keyboard, atouchscreen with “soft” buttons or with various components for use witha compatible stylus, a microphone by which a user may provide oralcommands to the exemplary controller 60 to be “translated” by a voicerecognition program, or other like device by which a user maycommunicate specific operating instructions to the exemplary controller.The operating interface 80 may be a part or a function of a graphicaluser interface (GUI) mounted on, integral to, or associated with, thedigital image forming device 10 with which the exemplary controller 60is associated.

The exemplary controller 60 may include one or more local processors 82for individually operating the exemplary controller 60 and for carryinginto effect control and operating functions for image formation onto aprint substrate 34, including rendering digital images, measuringcapacitance to determine thickness of fountain solution applied by afountain solution applicator on an imaging member surface and/ordetermine image forming device real-time image forming modifications forsubsequent printings. For example, in real-time during the printing of aprint job, based on the measured capacitance of the fountain solutionthickness, processors 82 may adjust image forming (e.g., fountainsolution deposition flow rate) to reach or maintain a preferred fountainsolution thickness on the imaging member surface for subsequent (e.g.,next) printings of the print job with the digital image forming device10 with which the exemplary controller may be associated. Processor(s)82 may include at least one conventional processor or microprocessorthat interprets and executes instructions to direct specific functioningof the exemplary controller 60, and control adjustments of the imageforming process with the exemplary controller.

The exemplary controller 60 may include one or more data storage devices84. Such data storage device(s) 84 may be used to store data oroperating programs to be used by the exemplary controller 60, andspecifically the processor(s) 82. Data storage device(s) 84 may be usedto store information regarding, for example, digital image information,printed image response data, fountain solution thickness correspondingto capacitance, an initial capacitance between capacitance sensor 58 andthe imaging member surface 26 before fountain solution deposition, atarget fountain solution thickness and corresponding capacitance, andother fountain solution deposition information with which the digitalimage forming device 10 is associated. Stored capacitance and fountainsolution thickness data may be devolved into data to generate arecurring, continuous or closed loop feedback fountain solutiondeposition rate modification in the manner generally described byexamples herein.

The data storage device(s) 84 may include a random access memory (RAM)or another type of dynamic storage device that is capable of storingupdatable database information, and for separately storing instructionsfor execution of image correction operations by, for example,processor(s) 82. Data storage device(s) 84 may also include a read-onlymemory (ROM), which may include a conventional ROM device or anothertype of static storage device that stores static information andinstructions for processor(s) 82. Further, the data storage device(s) 84may be integral to the exemplary controller 60, or may be providedexternal to, and in wired or wireless communication with, the exemplarycontroller 60, including as cloud-based data storage components.

The data storage device(s) 84 may include non-transitorymachine-readable storage medium used to store the device queue managerlogic persistently. While a non-transitory machine-readable storagemedium is may be discussed as a single medium, the term“machine-readable storage medium” should be taken to include a singlemedium or multiple media (e.g., a centralized or distributed database,and/or associated caches and servers) that store one or more sets ofinstructions. The term “machine-readable storage medium” shall also betaken to include any medium that is capable of storing or encoding a setof instruction for execution by the controller 60 and that causes thedigital image forming device 10 to perform any one or more of themethodologies of the present invention. The term “machine-readablestorage medium” shall accordingly be taken to include, but not belimited to, solid-state memories, and optical and magnetic media.

The exemplary controller 60 may include at least one data output/displaydevice 86, which may be configured as one or more conventionalmechanisms that output information to a user, including, but not limitedto, a display screen on a GUI of the digital image forming device 10 orassociated image forming device with which the exemplary controller 60may be associated. The data output/display device 86 may be used toindicate to a user a status of the digital image forming device 10 withwhich the exemplary controller 60 may be associated including anoperation of one or more individually controlled components at one ormore of a plurality of separate image processing stations or subsystemsassociated with the image forming device.

The exemplary controller 60 may include one or more separate externalcommunication interfaces 88 by which the exemplary controller 60 maycommunicate with components that may be external to the exemplarycontrol system such as capacitance sensor 58 (e.g., capacitive proximitysensor, non-contact displacement capacitive sensor) that can monitorfountain solution layer 32 thickness. At least one of the externalcommunication interfaces 88 may be configured as an input port tosupport connecting an external CAD/CAM device storing modelinginformation for execution of the control functions in the imageformation and correction operations. Any suitable data connection toprovide wired or wireless communication between the exemplary controller60 and external and/or associated components is contemplated to beencompassed by the depicted external communication interface 88.

The exemplary controller 60 may include an image forming control device90 that may be used to control an image correction process includingfountain solution deposition rate control and modification to renderimages on imaging member surface 26 having a desired fountain solutionthickness. For example, the image forming control device 90 may renderdigital images on the reimageable surface 26 having a desired fountainsolution thickness from fountain solution flow adjusted automatically inreal-time based on capacitive measurements of prior printings of thesame print job. The image forming control device 90 may operate as apart or a function of the processor 82 coupled to one or more of thedata storage devices 84 and the digital image forming device 10 (e.g.,optical patterning subsystem 16, inking apparatus 18, dampening station12), or may operate as a separate stand-alone component module orcircuit in the exemplary controller 60.

All of the various components of the exemplary controller 60, asdepicted in FIG. 4, may be connected internally, and to the digitalimage forming device 10, associated image forming apparatuses downstreamthe image forming device and/or components thereof, by one or moredata/control busses 92. These data/control busses 92 may provide wiredor wireless communication between the various components of the imageforming device 10 and any associated image forming apparatus, whetherall of those components are housed integrally in, or are otherwiseexternal and connected to image forming devices with which the exemplarycontroller 60 may be associated.

It should be appreciated that, although depicted in FIG. 4 as anintegral unit, the various disclosed elements of the exemplarycontroller 60 may be arranged in any combination of subsystems asindividual components or combinations of components, integral to asingle unit, or external to, and in wired or wireless communication withthe single unit of the exemplary control system. In other words, nospecific configuration as an integral unit or as a support unit is to beimplied by the depiction in FIG. 4. Further, although depicted asindividual units for ease of understanding of the details provided inthis disclosure regarding the exemplary controller 60, it should beunderstood that the described functions of any of theindividually-depicted components, and particularly each of the depictedcontrol devices, may be undertaken, for example, by one or moreprocessors 82 connected to, and in communication with, one or more datastorage device(s) 84.

The disclosed embodiments may include an exemplary method forcontrolling fountain solution thickness on an imaging member surface ofa rotating imaging member in a digital image forming device 10. FIG. 5illustrates a flowchart of such an exemplary method. As shown in FIG. 5,operation of the method commences at Step S100 and proceeds to StepS110.

At Step S110, a capacitive proximity sensor spatially offset a fixeddistance from the imaging member surface measures a first capacitancebetween the sensor and the imaging member surface having no fluidtherebetween. This measurement may also be referred to as a referencecapacitance or an initial capacitance that the image forming device 10needs to measure the fountain solution thickness. Operation of themethod proceeds to Step S120.

At Step S120, the fountain solution applicator 14 applies a fountainsolution fluid layer 32 at a dispense rate onto the imaging membersurface as part of the process for rendering a printing of a currentimage. Operation proceeds to Step S130.

At Step S130, the capacitive proximity sensor measures a secondcapacitance between the capacitive proximity sensor and the imagingmember surface with the fountain solution layer therebetween andspatially distanced from the capacitive proximity sensor.

Operation of the method proceeds to Step S140, where the controller orprocessor thereof compares a difference between the first capacitanceand the second capacitance to a predefined target capacitance. It isunderstood that the comparison may be between different capacitances orbetween different other units corresponding to capacitance. For example,the comparison may be between different fountain solution layerthicknesses where a difference between the first capacitance and thesecond capacitance corresponds to a fountain solution thickness and thepredefined target capacitance corresponds to a target fountain solutionthickness. It is also understood that the comparison to the predefinedtarget capacitance may be from a measurement of a single fountainsolution layer or from an average of a plurality of measurements of aplurality of fountain solution layers made during a rendering of aplurality of printings. The controller may store and average themeasured capacitances/fountain solution layer thicknesses over a periodand compare the average to the predefined target capacitance/fountainsolution thickness. Using average measurements may account for a smallvariance in fountain solution thickness across successive printingsallowed within manufacturing tolerances. The predefined targetcapacitance/fountain solution thickness information may be stored indata storage device 84 as depicted in FIG. 3 or as a lookup table.

Operation of the method proceeds to Step S150, where the controller 60modifies the fountain solution dispense rate based on the comparison forsubsequent printing using the modified fountain solution dispense rate.Operation may cease at Step S160, or may continue by repeating back toStep S120 where the fountain solution applicator 14 applies a subsequentfountain solution layer at the modified fountain solution dispense rateonto the imaging member surface as desired.

The exemplary depicted sequence of executable method steps representsone example of a corresponding sequence of acts for implementing thefunctions described in the steps. The exemplary depicted steps may beexecuted in any reasonable order to carry into effect the objectives ofthe disclosed embodiments. No particular order to the disclosed steps ofthe method is necessarily implied by the depiction in FIG. 5, and theaccompanying description, except where any particular method step isreasonably considered to be a necessary precondition to execution of anyother method step. Individual method steps may be carried out insequence or in parallel in simultaneous or near simultaneous timing.Additionally, not all of the depicted and described method steps need tobe included in any particular scheme according to disclosure.

Those skilled in the art will appreciate that other embodiments of thedisclosed subject matter may be practiced with many types of imageforming elements common to offset inking system in many differentconfigurations. For example, although digital lithographic systems andmethods are shown in the discussed embodiments, the examples may applyto analog image forming systems and methods, including analog offsetinking systems and methods. It should be understood that these arenon-limiting examples of the variations that may be undertaken accordingto the disclosed schemes. In other words, no particular limitingconfiguration is to be implied from the above description and theaccompanying drawings.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art.

What is claimed is:
 1. A method of controlling fountain solutionthickness on an imaging member surface of a rotating imaging member in adigital image forming device, comprising: a) measuring a firstcapacitance between a capacitive proximity sensor spatially offset afixed distance from the imaging member surface and the imaging membersurface having no fluid therebetween; b) applying a fountain solutionfluid layer at a dispense rate onto the imaging member surface upstreamthe capacitive proximity sensor in an image making direction forrendering a printing; c) measuring a second capacitance between thecapacitive proximity sensor and the imaging member surface with thefountain solution layer therebetween and spatially distanced from thecapacitive proximity sensor; d) comparing a difference between the firstcapacitance and the second capacitance to a predefined targetcapacitance; e) modifying the fountain solution dispense rate based onthe comparison; and f) applying a subsequent fountain solution layer atthe modified fountain solution dispense rate onto the imaging membersurface upstream the capacitive proximity sensor for rendering asubsequent printing.
 2. The method of claim 1, wherein the capacitiveproximity sensor is a non-contact displacement capacitive sensor.
 3. Themethod of claim 1, wherein the capacitive proximity sensor is anon-contact high resolution capacitive displacement sensor having aresolution high enough to measuring the second capacitance at nanometerscale thickness variance.
 4. The method of claim 1, wherein thedifference between the first capacitance and the second capacitancecorresponds to a fountain solution thickness and the predefined targetcapacitance corresponds to a target fountain solution thickness, and thestep d) comparing includes comparing the difference between the fountainsolution thickness and the target fountain solution thickness.
 5. Themethod of claim 1, wherein the capacitive proximity sensor is spatiallyoffset from the imaging member surface less than 750 microns.
 6. Themethod of claim 1, further comprising after step c), applying a secondfountain solution fluid layer at the dispense rate onto the imagingmember surface upstream the capacitive proximity sensor in the imagemaking direction for rendering a second printing, measuring a thirdcapacitance between the capacitive proximity sensor and the imagingmember surface with the second fountain solution layer therebetween,averaging the second capacitance and the third capacitance, and the stepd) comparing the difference compares the difference between the firstcapacitance and the average of the second and third capacitances.
 7. Themethod of claim 1, the rendering the printing including the digitalimage forming device applying the fountain solution layer at thedispense rate onto the imaging member surface, vaporizing in an imagewise fashion a portion of the fountain solution layer to form a latentimage, applying ink onto the latent image over the imaging membersurface, and transferring the applied ink from the imaging membersurface to a print substrate.
 8. The method of claim 7, the renderingthe subsequent printing including the digital image forming deviceapplying the subsequent fountain solution layer at the modified fountainsolution dispense rate onto the imaging member surface, vaporizing in animage wise fashion a portion of the subsequent fountain solution layerto form a subsequent latent image, applying ink onto the subsequentlatent image over the imaging member surface, and transferring theapplied ink from the imaging member surface to a subsequent printsubstrate.
 9. The method of claim 1, wherein the capacitive proximitysensor is spatially distanced from the imaging member surface to form agap therebetween, and the capacitive proximity sensor has a resolutionof about 0.001% of the gap.
 10. A method of controlling fountainsolution thickness on an imaging member surface of a rotating imagingmember in a digital image forming device, the digital image formingdevice printing a current image onto a print substrate, the printingincluding applying a fountain solution layer at a dispense rate onto theimaging member surface, vaporizing in an image wise fashion a portion ofthe fountain solution layer to form a latent image, applying ink ontothe latent image over the imaging member surface, and transferring theapplied ink from the imaging member surface to the print substrate, themethod comprising: a) measuring a capacitance between a capacitiveproximity sensor and the imaging member surface with the fountainsolution layer therebetween and spatially distanced from the capacitiveproximity sensor; b) comparing a difference between the measuredcapacitance and a reference capacitance between the imaging membersurface and the capacitive proximity sensor, to a target capacitance;and c) modifying the fountain solution dispense rate based on thecomparison for a subsequent printing of a subsequent image by thedigital image forming device using the modified fountain solutiondispense rate.
 11. The method of claim 10, wherein the capacitiveproximity sensor is a non-contact high resolution capacitivedisplacement sensor having a resolution high enough to measuring thesecond capacitance at nanometer scale thickness variance.
 12. The methodof claim 10, wherein the difference between the measured capacitance andthe reference capacitance corresponds to a fountain solution thicknessand the predefined target capacitance corresponds to a target fountainsolution thickness, and the step b) comparing includes comparing thedifference between the fountain solution thickness and the targetfountain solution thickness.
 13. The method of claim 10, furthercomprising after step b), applying a second fountain solution fluidlayer at the dispense rate onto the imaging member surface upstream thecapacitive proximity sensor in the image making direction for renderinga second printing, measuring a second capacitance between the capacitiveproximity sensor and the imaging member surface with the second fountainsolution layer therebetween, averaging the second capacitance and themeasured capacitance, and the step c) comparing the difference comparesthe difference between the reference capacitance and the average of thesecond and measured capacitances.
 14. The method of claim 10, therendering the subsequent printing including the digital image formingdevice applying the subsequent fountain solution layer at the modifiedfountain solution dispense rate onto the imaging member surface,vaporizing in an image wise fashion a portion of the subsequent fountainsolution layer to form a subsequent latent image, applying ink onto thesubsequent latent image over the imaging member surface, andtransferring the applied ink from the imaging member surface to asubsequent print substrate.
 15. A digital image forming devicecontrolling fountain solution thickness on an imaging member surface ofa rotating imaging member, comprising: a capacitance sensor distancedfrom the imaging member surface forming a gap therebetween, thecapacitance sensor configured to measure a first capacitance between thecapacitive proximity sensor and the imaging member surface, with theimaging member surface having no fluid therebetween; a fountain solutionapplicator configured to apply a fountain solution fluid layer at adispense rate onto the imaging member surface upstream the capacitiveproximity sensor in an image making direction for rendering a printing,the capacitance sensor configured to measure a second capacitancebetween the capacitive proximity sensor and the imaging member surfacewith the fountain solution layer therebetween and spatially distancedfrom the capacitive proximity sensor; and a controller in communicationwith the capacitance sensor to compare a difference between the firstcapacitance and the second capacitance to a predefined targetcapacitance, and modify the fountain solution dispense rate based on thecomparison, the fountain solution applicator configured to apply asubsequent fountain solution layer at the modified fountain solutiondispense rate onto the imaging member surface upstream the capacitiveproximity sensor for rendering a subsequent printing.
 16. The device ofclaim 15, wherein the capacitive proximity sensor is a non-contact highresolution capacitive displacement sensor having a resolution highenough to measuring the second capacitance at nanometer scale thicknessvariance.
 17. The device of claim 15, wherein the difference between thefirst capacitance and the second capacitance corresponds to a fountainsolution thickness and the predefined target capacitance corresponds toa target fountain solution thickness.
 18. The device of claim 15,wherein the capacitive proximity sensor is spatially offset from theimaging member surface less than 750 microns.
 19. The device of claim15, further comprising an optical patterning subsystem vaporizing in animage wise fashion a portion of the fountain solution layer to form alatent image, an inking apparatus applying ink onto the latent imageover the imaging member surface, and an image transfer stationtransferring the applied ink from the imaging member surface to theprint substrate.
 20. The device of claim 15, wherein the capacitiveproximity sensor has a resolution of about 0.001% of the gap.